It is common practice to filter various kinds of liquids when the liquids are administered by an intravenous unit to a patient. Generally, the liquid is passed through a filter housing containing a flat microporous hydrophilic membrane sealed to the walls of the filter housing and supported by a grid or the like.
It is also well known that when a hydrophilic membrane is wet (that is, when the pores are filled with the liquid being filtered), air or other gas cannot pass through the membrane except under increased pressure. Hence, if there is air or other gas in the liquid being filtered, it accumulates on the inlet surface of a membrane and blocks or interferes with the passage of liquid through the membrane. It is also necessary to prevent the air from flowing in the liquid to the patient. Therefore, it is necessary to remove the air, as well as other particulates, from the liquid while also removing the air from the filter housing.
With specific regard to initiating the intravenous fluid flow, most systems require various manipulations to simultaneously prime the filter housing with the liquid while removing air that is trapped within the filter housing on the inlet side and outlet side of the membrane.
Additionally, it is quite useful to determine whether or not air remains trapped in a filter housing during liquid flow through the housing.
The U.S. Pat. Nos. 4,111,807 to Boomus et al., issued Sep. 5, 1978; 4,319,996 to Vincent et al., issued Mar. 16, 1982; and 4,369,112 to Vincent et al., issued Jan. 18, 1983, all relate to various filter assemblies for use in intravenous administration settings. Each of these assemblies do not include any means for allowing simple priming of the assembly to remove air therefrom, nor do they provide any means for simply and readily indicating air remaining in the system once liquid is flowing therethrough.